Pharmacology
Pharmacology: what is tested
The exam tests pharmacokinetics, autonomic drugs, local anesthetics, analgesics, antimicrobials, and dental prescribing. Calculations and safety limits are common.
Core rules
- Bioavailability is the fraction reaching systemic circulation; first-pass metabolism reduces oral bioavailability.
- Half-life determines dosing interval; clearance determines maintenance dose; volume of distribution determines loading dose.
- Zero-order kinetics occurs when elimination capacity is saturated, as with ethanol, phenytoin, and high-dose aspirin.
- Local anesthetics are weak bases; the uncharged form crosses the nerve membrane. In inflamed acidic tissue, more drug is ionized, so anesthesia is weaker.
- Lidocaine maximum dose is about 4.4 mg/kg without vasoconstrictor and 7 mg/kg with epinephrine.
- Epinephrine prolongs anesthesia and reduces systemic absorption but is used cautiously in severe cardiovascular disease.
- NSAIDs inhibit cyclooxygenase; aspirin irreversibly acetylates platelet COX-1.
- Antibiotic prophylaxis for at-risk cardiac patients is usually amoxicillin 2 g orally 30-60 minutes before the procedure; clindamycin is a substitute for penicillin allergy.
Worked example
A 60 kg patient needs lidocaine with epinephrine. Reasoning: maximum dose is 7 mg/kg, so 60 x 7 = 420 mg. A 2 percent solution contains 20 mg/mL, so 420 / 20 = 21 mL. This is a safety ceiling, not a target; the smallest effective volume should be used.
Traps
- Calculating dose from the cartridge volume without checking the percentage.
- Expecting good anesthesia in acute inflammation with a standard pKa drug.
- Confusing half-life with duration of action.
- Forgetting that aspirin effect lasts for the platelet lifespan.